Available on the Commodore C64/C128. Software emulated. The signals does not have true RS232 levels. It's TTL level, and RXD/TXD is inverted. It's just the normal User Port, used as a RS232 port.
 (at the computer)
 (at the computer)
UNKNOWN CONNECTOR at the computer.
| Pin | Name | RS232 | Description | 
|---|---|---|---|
| A | GND | GND | Protective Ground | 
| B+C | FLAG2+PB0 | RxD | Receive Data (Must be applied to both pins!) | 
| D | PB1 | RTS | Ready To Send | 
| E | PB2 | DTR | Data Terminal Ready | 
| F | PB3 | RI | Ring Indicator | 
| H | PB4 | DCD | Data Carrier Detect | 
| K | PB6 | CTS | Clear To Send | 
| L | PB7 | DSR | Data Set Ready | 
| M | PA2 | TxD | Transmit Data | 
| N | GND | GND | Signal Ground | 
| Contributor: | Joakim Ögren, Arwin Vosselman, Mark Sokos | 
| Source: | Usenet posting in comp.sys.cbm - Help on modem -> c64 by Lasher Glenn | 
| Commodore 64 Programmer's Reference Guide | 
  Copyright © The Hardware Book Team 1996-2004.
  May be copied and redistributed, partially or in whole, as appropriate.
  Document last modified: 2002-01-10